Functions registered with ExternalInterface.addCallback not available in Javascript

Question

I'm working on a Flash game that needs to call some Javascript on the page and get data back from it. Calling Javascript from Flash works. Calling the Flash functions from Javascript (often) doesn't.

I'm using the Gaia framework.

What happens:

1. The swf is loaded in with SWFObject
2. There's a button in the Flash file. On click, it uses ExternalInterface.call() to call a Javascript function. This works.
3. The Javascript function calls a Flash function that was exposed with ExternalInterface.addCallback().
4. Sometimes, the Javascript produces the following error: TypeError: myFlash.testCallback is not a function.
5. When the error happens, it affects all functions registered with addCallback(). Gaia and some of its included libraries use addCallback(), and calling those functions from Javascript also produces the TypeError.
6. Waiting a long time before pressing the button in Flash doesn't solve the error.
7. Having Flash re-try addCallback() periodically doesn't solve the error
8. When the error occurs, ExternalInterface.available = true and ExternalInterface.objectID contains the correct name for the Flash embed object.
9. When the error occurs, document.getElementById('myflashcontent') correctly returns the Flash embed object.

Edited to add:

• This issue shows up in Firefox 3.6, but not Chrome or IE8. I haven't tried older browsers.
• I'm running the Debug version of the Flash player.
• My calls to ExternalInterface.addCallback() are wrapped in a try...catch block. When the JS error occurs, the catch block is not triggered. It's a silent failure.
• The error occurs when testing on a webhost, with the swf loaded from the same server as the page it's on.
• I set allowScriptAccess = always.
• Setting flash.system.Security.allowDomain("mydomain") doesn't fix the error.

From my Page class:

public class MyPage extends AbstractPage
{
    // declarations of stage instances and class variables

    // other functions

    override public function transitionIn():void 
    {
        send_button.addEventListener(MouseEvent.MOUSE_UP, callJS);
        exposeCallbacks();

        super.transitionIn();
    }

    private function exposeCallbacks():void
    {
        trace("exposeCallbacks()");
        if (ExternalInterface.available) {
            trace("ExternalInterface.objectID: " + ExternalInterface.objectID);
            try {
                ExternalInterface.addCallback("testCallback", simpleTestCallback);
                trace("called ExternalInterface.addCallback");
            }
            catch (error:SecurityError) {
                trace("A SecurityError occurred: " + error.message + "\n");
            }
            catch (error:Error) {
                trace("An Error occurred: " + error.message + "\n");
            }
        }
        else {
            trace("exposeCallbacks() - ExternalInterface not available");
        }
    }

    private function simpleTestCallback(str:String):void
    {
        trace("simpleTestCallback(str=\"" + str + "\")");
    }

    private function callJS(e:Event):void
    {
        if (ExternalInterface.available) {
            ExternalInterface.call("sendTest", "name", "url");
        }
        else {
            trace("callJS() - ExternalInterface not available");
        }
    }

}

My Javascript:

function sendTest(text, url) {
    var myFlash = document.getElementById("myflashcontent");

    var callbackStatus = "";
    callbackStatus += '\nmyFlash[testCallback]: ' + myFlash['testCallback'];
    //console.log(callbackStatus);

    var errors = false;
    try {
        myFlash.testCallback("test string");
    }
    catch (err) {
        alert("Error: " + err.toString());
        error = true;
    }

    if (!error) {
        alert("Success");
    }
}

var params = {
    quality: "high",
    scale: "noscale",
    wmode: "transparent",
    allowscriptaccess: "always",
    bgcolor: "#000000"
};
var flashVars = {
    siteXML: "xml/site.xml"
};
var attributes = {
    id: "myflashcontent",
    name: "myflashcontent"
};

// load the flash movie.
swfobject.embedSWF("http://myurl.com/main.swf?v2", "myflashcontent",
"728", "676", "10.0.0", serverRoot + "expressInstall.swf",
flashVars, params, attributes, function(returnObj) {
    console.log('Returned ' + returnObj.success);
    if (returnObj.success) { returnObj.ref.focus(); }
});

Answer 1

Calls made to JS via ExternalInterface are wrapped within a try { } block and that causes subsequent JS errors to get suppressed.

A workaround for the same is to cause a function closure in JavaScript and execute the actual code after a timeout.

Example:

function myFnCalledByEI (arg1, arg2) {

    setTimeout(myActualFunction () {
       // You can use arg1 and arg2 here as well!
       // Errors raised within this function will not be
       // suppressed.
    }, 0);

};